An example of a piston for an internal combustion engine, wherein ribs are formed radially on the reverse surface of a crown part of the piston, stresses concentrated on the crown part are alleviated, and the thickness and weight of the crown part is reduced, is proposed in Japanese Patent Laid-Open Publication No. 2005-133613. This piston for an internal combustion engine will be described based on FIG. 10 hereof.
As shown in FIG. 10, a piston 200 is molded as an integrated member having: a crown part 201; a cylindrical land part 202 that extends downward from the edge of the crown part 201; cylindrical skirt parts 203, 203 that extend further downward from the land part 202; a cup-shaped support 208 that is formed on a reverse surface 207 of the crown part 201 in order to slidably link to a small end 206 of a con rod 204; and a plurality of ribs 211 that extend downward from the reverse surface 207 of the crown part 201.
The aforementioned cup-shaped support 208 has a narrow fixed base on the side of the crown part 201 and is shaped so that the diameter gradually increases from the fixed base. Therefore, when the piston 200 is to be formed by casting, a die with a plurality of partitions is used. Productivity decreases because the partitioned die must be dismantled when removing the piston element from the partitioned die. A method of manufacture that offers better productivity than casting has been needed.
Additionally, the piston 200 needs to be made lighter in order for the internal combustion engine to achieve higher rotation speeds.
Accordingly, a need has existed for a piston for an internal combustion engine offering improved productivity and lighter weight.